1. Field of the Invention
The present invention relates to a system and method for controlling intake air to an internal combustion engine by unthrottled intake air control.
2. Terminology
Engine Displacement
This is used herein to mean the sum of displacements of all of cylinders of an engine. xe2x80x9cEngine displacementxe2x80x9d and xe2x80x9cdisplacement of an enginexe2x80x9d are synonyms. In the description, the reference character xe2x80x9cVOL#xe2x80x9d is used to represent the xe2x80x9cengine displacementxe2x80x9d.
3. Description of Related Art
JP-A 8-200025 discloses a system for controlling electromagnetic drivers (EMDs) for intake and exhaust valves provided per each combustion chamber of an internal combustion engine. According to this system, an electronic control unit (ECU) controls valve timings of intake and exhaust valves independently from the crankshaft position and speed in one of predetermined schedules fit for various engine operation ranges. The ECU identifies which one of the various engine operation ranges against varying engine load and engine speed. During transient period from one to another of the engine operation ranges, the ECU shifts the valve timings of intake valves in a gradual manner so as to prevent occurrence of a rapid change in intake air characteristic. This JP-A is silent as to how engine load is controlled and has no teaching with regard to engine load control by early or delayed valve closure timings of the intake valves.
The present invention aims at controlling intake air by varying valve closure timings of intake valves using such EMDs. The electromagnetic drivers can adjust the valve opening and closure timings over a wide range independently from the crankshaft position. Since throttling of intake air is not relied upon to control the engine load, the engine pumping losses are eliminated.
EP 0 953 750 A2, published on November 3, teaches variably adjusting an angular opening angle of a throttle valve to maintain a predetermined negative pressure within an intake manifold downstream of the throttle valve during engine load control by unthrottled intake air control using variable adjustment of intake valve timing. The negative pressure within the intake manifold is needed for purge control. Due to the limitation of speed at which an EMD can move its intake valve, adjustment of valve closure timing becomes ineffective in intake air control in certain operation range. In such operation range, the throttle valve is relied upon to conduct throttled intake air control.
Because of the provision of intake manifold and collector downstream of a throttle valve, there is a delay, during throttled intake air control, between a change in angular position of the throttle valve and a change in cylinder air charge. In the case of unthrottled intake air control, there is no delay caused due to the intake manifold and collector so that a change in valve closure timing induces a change in cylinder air charge without any delay, providing aggressive response performance. For example, operator aggressive repetition of a cycle of depression and release of accelerator pedal induces such violent variation of torque imparted to a power train induces as to cause vibration, providing a reduction in ride comfort and a considerably high level of noise.
As mentioned above, unthrottling intake air control cannot control cylinder air charge satisfactorily in certain operation range. In such operation range, throttling of intake air by a throttle valve is needed. In such case, care must be taken to provide a smooth take over during transient period from the unthrottled control to the throttled control or vice versa without any shock due to a torque change. Undesired torque change might take place during such transient period due mainly to a considerable difference in response performance between the two control modes.
Thus, a need remains to improve an unthrottled intake air control by variable valve timing such that the occurrence of violent torque variation caused by aggressive cyclic depression and release manipulation of an accelerator pedal is prevented and the undesired torque change during transient period from one to the other of the two intake air control mode is suppressed.
It is an object of the present invention to provide a system and method for controlling intake air to an internal combustion engine such that the occurrence of violent torque variation caused by aggressive cyclic depression and release manipulation of an accelerator pedal is prevented and the undesired torque change during transient period from one to the other of the two intake air controls is suppressed.
According to one aspect of the present invention, there is provided a method for controlling intake air of an internal combustion engine, the engine having at least one combustion chamber provided with intake means together with an intake manifold provided with a throttle valve, wherein the opening and closure timings of the intake means are adjustable entirely independently from the crankshaft position to control the amount of intake air supplied to the combustion chamber, the method comprising:
providing a response adjustment to valve timing control of the intake means for unthrottled intake air control and throttle position control of the throttle valve for unthrottled intake air control.
According to another aspect of the present invention, there is provided a system for controlling intake air of an internal combustion engine, the engine having at least one combustion chamber provided with intake means together with an intake manifold provided with a throttle valve, wherein the opening and closure timings of the intake means are adjustable entirely independently from the crankshaft position to control the amount of intake air supplied to the combustion chamber, the method comprising:
a control for providing a response adjustment to valve timing control of the intake means for unthrottled intake air control and throttle position control of the throttle valve for unthrottled intake air control